1. Technical Field
This invention relates generally to a diesel engine adapted for operation in a homogenous charge compression ignition (HCCI) combustion mode and to a method for controlling HCCI combustion in a diesel engine, and more particularly, to such an engine and method that uses water injection to control the start of combustion in the HCCI mode.
2. Background Art
Homogenous charge compression ignition (HCCI) is a combustion mode in which a homogenous air-fuel mixture starts reaction in an engine combustion chamber when the full auto-ignition temperature is reached within the mixture. The reaction is initiated throughout the entire mixture, i.e., multi-point ignition, and proceeds without a visible flame front. U.S. Pat. No. 5,875,743 granted Mar. 2, 1999, to Daniel W. Dickey, one of the co-inventors of the present invention, titled APPARATUS AND METHOD FOR REDUCING EMISSIONS IN A DUAL COMBUSTION MODE DIESEL ENGINE, and assigned to the assignee of the present invention, describes the control of diesel engine emissions in a diesel engine adapted for at least partial operation in an HCCI combustion mode. U.S. Pat. No. 5,875,743 proposes the use of two fuel injectors, and optionally a water injector, for respective fuel and water injection based on engine operating parameters indicative of engine speed and load. U.S. Pat. No. 5,832,880 granted Nov. 10, 1998, also to Daniel W. Dickey, for an APPARATUS AND METHOD FOR CONTROLLING HOMOGENOUS CHARGE COMPRESSION IGNITION COMBUSTION IN DIESEL ENGINES, and likewise assigned to the assignee of the present invention, also describes controlling HCCI combustion by water injection.
However, there remain problems in providing a more precise control of HCCI combustion. More particularly, controlling the HCCI combustion process has presented two significant challenges:
1) controlling the combustion phasing with respect to the top dead center (TDC) position of a piston reciprocatively disposed in the combustion chamber, and
2) controllably extending the operating range of HCCI combustion into high engine loads.
The present invention is directed to overcoming the problems of controlling HCCI combustion with respect to TDC and extending HCCI combustion to high engine load conditions.
In accordance with one aspect of the present invention, a method for controlling homogenous charge compression ignition combustion in a diesel engine includes sensing pressure in the combustion chamber, sensing the angular position of the crankshaft with respect to a TDC position of a piston disposed in the combustion chamber, and calculating the values of a combustion chamber pressure derivative with respect to the crankshaft angle at a first time and at a subsequent second time. The change in values of the combustion chamber pressure derivative with respect to the crankshaft angle at the second time is compared with that of the first time, and a signal is delivered to a trigger circuit in response to the value of the combustion chamber pressure derivative with respect to the crankshaft angle at the second time being less than the value of the combustion chamber pressure derivative with respect to the crankshaft angle at the first time. Water is injected into the combustion chamber in response to the trigger circuit delivering a signal to a water injector.
In accordance with another aspect of the present invention, a method for controlling homogenous charge compression ignition combustion in a diesel engine includes sensing an operating characteristic representative of a first combustion stage. The injection of water into the combustion chamber subsequent to sensing the operating characteristic representative of the first combustion stage. Injecting water is carried out at a time, and for a length of time, sufficient to delay the start of a second combustion stage until a piston disposed in the combustion chamber is at a preselected position.
In accordance with yet another aspect of the present invention, a diesel engine adapted for at least partial operation in a homogenous charge compression ignition combustion mode has a means for sensing pressure in a combustion chamber of the engine, a means for sensing crankshaft angle, and a differentiator operatively connected to the means for sensing pressure in the combustion chamber and to the means for sensing crankshaft angle. A comparator is adapted to receive a signal from the differentiator, and a trigger circuit is adapted to receive a signal from the comparator. The diesel engine also includes an injector operatively connected to a source of water and adapted to inject water into the combustion chamber in response to receiving a signal from the trigger circuit.